[Clang][Sema] Refactor category declaration under CheckForIncompatibleAttributes. NFC

[eopXD]

Summary

This change would allow extension of new categories be aware of adding
more code here.

This patch also updates the comments, which was originally missing the
vector predicate.

[eopXD]

Upon modification to this code base I am tempt to prefer having a NumberOfCategories under the enum and make the sanity check explicit. I understand this is totally a problem of personal taste so definitely feel free to argue with me :)

[aaron.ballman]

This seems reasonable to me, but I'll leave the final sign-off to Erich.

clang/lib/Sema/SemaStmtAttr.cpp

335–336

Might as well rely on value initalization instead of a runtime call to memset.

[shafik]

clang/lib/Sema/SemaStmtAttr.cpp

319

Can you break up this comment, I think it should go above the enum and each one that is specific to an enumerator should go above that enumerator.

335–336

You can use {} to initialize the array. This will value-initialize each element, which for pointers will set it to zero.

[erichkeane]

I haven't dealt much with the loop hint attributes, but two of my coworkers have done extensive work in our downstream (@jyu2 and @mikerice), and likely have feedback about how this affects downstream feedback.

[eopXD]

Address comments from reviewers.

[eopXD]

Minor update in comments.

[mikerice]

In D137570#3921879, @erichkeane wrote:

I haven't dealt much with the loop hint attributes, but two of my coworkers have done extensive work in our downstream (@jyu2 and @mikerice), and likely have feedback about how this affects downstream feedback.

Looks good to me.

[jyu2]

It is okay with me.

[eopXD]

@mikerice @jyu2
May you accept the revision please if this patch looks good to you? Thank you :)

[eopXD]

Rebase to latest main.

clang/lib/Sema/SemaStmtAttr.cpp

CheckForIncompatibleAttributes(Sema &S,
   // on them, so skip all of the checking in the common case.
   if (Attrs.size() < 2)
     return;
 
   // First, check for the easy cases that are table-generated for us.
   if (!DiagnoseMutualExclusions(S, Attrs))
     return;
 
-  // There are 6 categories of loop hints attributes: vectorize, interleave,
-  // unroll, unroll_and_jam, pipeline and distribute. Except for distribute they
-  // come in two variants: a state form and a numeric form.  The state form
-  // selectively defaults/enables/disables the transformation for the loop
-  // (for unroll, default indicates full unrolling rather than enabling the
-  // transformation). The numeric form provides an integer hint (for
-  // example, unroll count) to the transformer. The following array accumulates
-  // the hints encountered while iterating through the attributes to check for
-  // compatibility.
+  enum CategoryType {
+    // For the following categories, they come in two variants: a state form and
+    // a numeric form. The state form may be one of default, enable, and
+    // disable. The numeric form provides an integer hint (for example, unroll
+    // count) to the transformer.
+    Vectorize,
+    Interleave,
+    UnrollAndJam,
+    Pipeline,
+    // For unroll, default indicates full unrolling rather than enabling the
+    // transformation.
+    Unroll,
+    // The loop distribution transformation only has a state form that is
+    // exposed by #pragma clang loop distribute (enable | disable).
+    Distribute,
+    // The vector predication only has a state form that is exposed by
+    // #pragma clang loop vectorize_predicate (enable | disable).
+    VectorizePredicate,
+    // This serves as a indicator to how many category are listed in this enum.
+    NumberOfCategories
+  };
+  // The following array accumulates the hints encountered while iterating
+  // through the attributes to check for compatibility.
   struct {
     const LoopHintAttr *StateAttr;
     const LoopHintAttr *NumericAttr;
-  } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
-                   {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
-                   {nullptr, nullptr}};
+  } HintAttrs[CategoryType::NumberOfCategories] = {};
 
   for (const auto *I : Attrs) {
     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
 
     // Skip non loop hint attributes
     if (!LH)
       continue;
 
+    CategoryType Category = CategoryType::NumberOfCategories;
     LoopHintAttr::OptionType Option = LH->getOption();
-    enum {
-      Vectorize,
-      Interleave,
-      Unroll,
-      UnrollAndJam,
-      Distribute,
-      Pipeline,
-      VectorizePredicate
-    } Category;
     switch (Option) {
     case LoopHintAttr::Vectorize:
     case LoopHintAttr::VectorizeWidth:
       Category = Vectorize;
       break;
     case LoopHintAttr::Interleave:
     case LoopHintAttr::InterleaveCount:
       Category = Interleave;
for (const auto *I : Attrs) {
     case LoopHintAttr::PipelineInitiationInterval:
       Category = Pipeline;
       break;
     case LoopHintAttr::VectorizePredicate:
       Category = VectorizePredicate;
       break;
     };
 
-    assert(Category < sizeof(HintAttrs) / sizeof(HintAttrs[0]));
+    assert(Category != NumberOfCategories && "Unhandled loop hint option");
     auto &CategoryState = HintAttrs[Category];
     const LoopHintAttr *PrevAttr;
     if (Option == LoopHintAttr::Vectorize ||
         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
         Option == LoopHintAttr::UnrollAndJam ||
         Option == LoopHintAttr::VectorizePredicate ||
         Option == LoopHintAttr::PipelineDisabled ||
         Option == LoopHintAttr::Distribute) {